Abstract

The uptake of HNO3, H2O, NO2 and NO was studied on meteoric smoke particle analogues using a low-pressure Knudsen cell operating at 295 K. The analogues used were olivine (MgFeSiO4) and a haematite/goethite (Fe2O3/FeO(OH)) mixture synthesised by the sol–gel process. For uptake on MgFeSiO4, the following uptake coefficients were obtained: γ(HNO3)=(1.8±0.3)×10−3, γ(H2O)=(4.0±1.3)×10−3, γ(NO2)=(5.7±0.2)×10−4 and γ(NO)<3×10−4. γ(HNO3) did not show a dependence on the mass of MgFeSiO4 in the Knudsen cell (when varied by a factor of 6) implying that, because of relatively efficient uptake, HNO3 is removed only by near-surface particles. This was corroborated by application of a surface uptake model. Saturating the MgFeSiO4 particles with water vapour before exposing them to NO2 increased γ(NO2) to (2.1±0.7)×10−3, but had a very small effect on γ(HNO3). For uptake on Fe2O3/FeO(OH), γ(HNO3)=(1.5±0.2)×10−3. These results were then included in a whole atmosphere chemistry–climate model, which shows that the heterogeneous removal on meteoric smoke particles in the winter polar vortex between 30 and 60 km appears to provide an important sink for HNO3.